Field of the Invention
The present invention relates to a heat exchanger and a water heater including the heat exchanger.
Description of the Background Art
A heat exchanger is mainly constituted of a plurality of plate-shaped fins, a heat conduction pipe passing through the fins, a water supply pipe and a hot water delivery pipe connected to the heat conduction pipe, a shell plate serving as an exterior, and the like. In a water heater, for example, a burner sending a combustion gas to the heat exchanger is arranged in a lower portion of the heat exchanger. The heat conduction pipe is arranged as one connected pipe, on a side closer to the burner (a lower stage) and on a side farther therefrom (an upper stage), such that it extends back and forth through the fins. The water supply pipe is connected to one end side of the heat conduction pipe such that water flows from the heat conduction pipe arranged in the lower stage closer to the burner to the heat conduction pipe arranged in the upper stage, and the hot water delivery pipe is connected to the other end side located opposite thereto.
In the heat exchanger, in a cross-section in a direction substantially orthogonal to a direction of extension of the heat conduction pipe, when the heat conduction pipe is arranged such that the number of heat conduction pipes (cross-sections) arranged in the lower stage is the same as the number of heat conduction pipes (cross-sections) arranged in the upper stage, the heat conduction pipe is arranged such that the cross-sections of the heat conduction pipe are disposed in grids. On the other hand, when the heat conduction pipe is arranged such that the number of heat conduction pipes (cross-sections) arranged in the lower stage is different from the number of heat conduction pipes (cross-sections) arranged in the upper stage, the heat conduction pipe is arranged such that the cross-sections of the heat conduction pipes are disposed as staggered.
Japanese Patent Laying-Open No. 2006-349234, Japanese Utility Model Laying-Open No. 03-546, and Japanese Patent Laying-Open No. 08-200819 each disclose such a heat exchanger that a heat conduction pipe is arranged in a lower stage and an upper stage.
Conventionally, in particular in a heat exchanger adopting such an arrangement that a heat conduction pipe is disposed in grids in a lower stage and an upper stage, when a pitch between heat conduction pipes arranged in the lower stage is the same as a pitch between heat conduction pipes arranged in the upper stage, a portion directly under the heat conduction pipe in the upper stage located downstream of a flow of a combustion gas is hidden behind the heat conduction pipe in the lower stage. Therefore, the combustion gas cannot be in efficient contact with the heat conduction pipe and further improvement in heat exchanger effectiveness between water and the combustion gas in the heat exchanger is interfered.